As such a drilling tool, one in which an annular ring bit is provided at a leading end of a circular-cylindrical casing pipe so as to be rotatable around an axis of the casing pipe, and a pilot bit (inner bit) is attached to a leading end of the transmission member inserted into the casing pipe is known. For example, Patent Document 1 suggests a drilling tool in which first and second abutment parts capable of abutting the casing pipe and the ring bit, respectively, are formed toward a leading end side in an axis direction at the outer periphery of the pilot bit, the pilot bit is engageable with the ring bit around the axis, and the ring bit is removable from the casing pipe to the leading end side in the axis direction.